1. Field of the Invention
The present invention relates to a packaging for radioactive materials. More particularly, it relates to a packaging in which a shielding material is buried and a method of manufacturing such packaging.
2. Description of the Prior Art
A conventional packaging for radioactive materials has a resin layer on the surface of its shell made of forged steel in order to prevent neutrons from streaming out of the packaging. The packaging also has a plurality of fins projecting to the outside through the resin layer in order to dissipate heat from the radioactive materials therein. Since portions of the surface of the shell on which the fins pass through the resin layer lack the resin layer, some neutrons inevitably stream to the outside. Another conventional packaging is provided with hollows in its shell made of cast steel or forged steel and these hollows are filled with resins to shield neutrons. Such hollows are formed by extraordinary deep hole machining which is both troublesome and labor consuming.
On the other hand, as a neutron shielding material, boron nitride or boron carbide has been used. As a neutron moderator accelerating the neutron absorbence of the shielding material, hydrogen-rich materials such as water, paraffin, wood, resin, or concrete have been known. However, when these materials are used as a shielding material for exothermic radioactive materials, they can only be positioned at a certain location because of the lack of heat-resistance and thermal conductivity.
Materials having a boron exhibit a shielding effect against the thermal neutron characteristic zone alone. Materials containing hydrogen as a neutron moderator are required for a dry-type transportation packaging or a dry-type storage packaging for nuclear fuels containing fast neutron, and thus, has to be excellent in terms of both heat-resistance and thermal conductivity characteristics. Materials such as synthetic resins are generally used. Since the resins lack both heat-resistance and thermal conductivity, they should be used together with aluminum and/or carbon to supplement these defects.